DESCRIPTION OF THE RELATED ART
Devant and Braun (Chem. Berichte 119 (1986) 2191-2207) describe the impossibility of eliminating chiral amines from acetamides without destroying the center of chirality (page 2194). The authors were furthermore unsuccessful in numerous attempts to hydrolyze the amides with alkali or acid to the carboxylic acid and optically active amine, and they found that the required result was achieved only by reaction with dinitrogen tetroxide as described by White (J. Am. Chem. Soc. 77 (1955) 6008). However, this reaction with N.sub.2 O.sub.4 is elaborate and therefore unsuitable for industrial processes.
WO 95/08636 describes an enzymatic process for resolving optically active amines in which the amines are enantioselectively acylated with an ester, then the mixture of acylated amine (amide) and unreacted amine is separated and, where appropriate, the optically active amine is liberated from the acylated amine (amide) by amide cleavage. However, no possible parameters for the amide cleavage process are indicated.
As a continuation of this process, PCT/EP/96/03948 describes a process for cleaving optically active amides to carboxylic acids and optically active amines with retention of the center of chirality, which comprises hydrolyzing the amides in the presence of a polyol or amino alcohol and of an alkali metal or alkaline earth metal hydroxide.
The carboxylic acids employed in this case as auxiliary reagent for the enzymatic resolution of optically active amines are preferably .alpha.-, .beta.- or .gamma.-substituted carboxylic acids which are, as a rule, used as aqueous solution which, besides a salt or an ester of the above carboxylic acid, contains at least one polyol or at least one amino alcohol and an alkali metal or alkaline earth metal hydroxide. The solutions have hitherto always been fed to an incinerator.
Fractionation of a mixture of this type by distillation is usually impossible because the carboxylic acids or their salts or esters are able to react to esterify the polyol, eg. ethylene glycol (EG) or diethylene glycol (DEG), or the amino alcohol, eg. ethanolamine, diethanolamine and triethanolamine (TEA) and/or to form a salt (in the case of TEA). Accordingly, to optimize the yield, it is previously necessary to remove as far as possible the abovementioned components present besides the carboxylic acid or the salt or ester thereof. Workup by distillation is generally difficult or industrially very elaborate because of the high boiling points of the abovementioned compounds. It has also to be taken into account that ethylene glycol, for example, has a similar boiling point to many of the carboxylic acids under discussion here, eg. methoxyacetic acid, which in turn makes removal of the acid from the above mixture by distillation difficult.